


Song As Old As Rhyme

by doctormccoy, jokerswild



Category: The Hobbit (Jackson Movies), The Hobbit - All Media Types, The Hobbit - J. R. R. Tolkien
Genre: Accidental Breathplay, Anal Sex, Fisherman!Fili, Interspecies Sex, Language Barrier, M/M, Mate trope, Mermaid!Kili, Mermaids, No Incest, Rimming, Shameless Smut, Siren song
Language: English
Status: Completed
Published: 2013-08-11
Updated: 2013-08-11
Packaged: 2017-12-22 16:16:26
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 13,753
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/915331
Author URL: https://archiveofourown.org/users/doctormccoy/pseuds/doctormccoy, https://archiveofourown.org/users/jokerswild/pseuds/jokerswild
Summary: <blockquote class="userstuff">
              <p>Fíli will never understand why his Father is so enamored of the strange creature named Thorin, until one day he meets Thorin's nephew, and everything changes.</p>
            </blockquote>





	Song As Old As Rhyme

**Author's Note:**

> Inspired by the beautiful Mer!Au artworks by [kyuubikun](http://kyuubikun.tumblr.com/), [ladynorthstar](http://ladynorthstar.tumblr.com/) and all the other lovely artists on tumblr who've drawn for this theme!
> 
> Fíli is written by thorinoakenshield and Kíli is written by jokerswild.
> 
> Kíli is a [clownfish!mer](http://www.okeanosgroup.com/blog/wp-content/uploads/2012/06/Oceans-Clownfish.jpg).
> 
> Fish don't have dicks so Kíli has something akin to what dolphins have, as seen [here](http://ladynorthstar.tumblr.com/post/57377381848/i-was-researching-on-dolphins-anatomy-for-the-sake).
> 
> Also the "glowing strings" are glow worms, which are technically found only in New Zealand but have been appropriated in Wales for this story. Sorry, science.

Kíli has never seen what's so interesting about humans or at the very least the human, _Dwalin_ his Uncle Thorin had said, in particular. The mer had met the man once and had automatically questioned his sanity. He didn't understand the attraction his Uncle so obviously felt and had been a little worried about the man being a fisherman. He'd been told to leave the pair alone though, both by his mother and by Thorin, but that had been before the whole whale incident. 

Both his guardians had argued all day yesterday about what to do with the young mer today. His Uncle always met Dwalin and helped him fish during calm days but his mother needed a break from her mischievous son. It wasn't like Kíli had _meant_ to fall asleep on that migrating whale, and he was adult, he could watch out for himself. Neither guardian wanted to hear it though and after a short standoff, Thorin had given in, agreeing to take his nephew with him today.

So that's how Kíli found himself swimming in lazy circles underneath the boat, deep enough that he didn't have to hear whatever they were saying. He didn't understand as much of the language as his Uncle but that didn't mean he didn't know when the pair were being flirty and generally pretty embarrassing for creatures their ages. Well, actually the young mer didn't know exactly how old _Dwalin_ was but he's pretty sure it's old enough to not need help with fishing.

The brunet sighs long and loud through his gills, just enough for his Uncle to hear, and is met with a piercing glare from the other mer. Kíli motions for Thorin to hurry up but his Uncle simply ignores him and pops his head back above the water to keep talking to his human. After another few rounds under the boat, Kíli decides he's had enough and swims up to the other side of the boat, fully intending on stealing something from Dwalin and making off with it.

He's quick and quiet as he approaches the other side of the boat and just as he peeks over the side he sees that Dwalin isn't alone in the boat. There's a human with him, with blond hair and considerably younger than the other. A pair of blue eyes meet his and with one quick movement of his tail, Kíli is sinking back into the depths of the water, staring up at the surface.

Fíli had to admit, his Father's obsession with the strange creature that lived beneath the water was a little, well... strange. When he'd first confessed the love affair to him, Fíli had been convinced that losing his mother had finally pushed his Father over the edge into insanity. Sailors would always come into the city Fíli had once called home and boast about seeing beautiful women in the water, but, surely there was really no such thing as mermaids.

The next morning he had joined Dwalin to go fishing and met the thing himself, a mind boggling combination of man and fish that he was still half convinced he'd imagined. The stress of moving to the countryside, perhaps. 

Things had been hard since they had come to the tiny village on the coast of Wales, far from London where Fíli had been born and raised. His mother had been murdered a little over a year ago by men who wanted her jewelry, and by the end of the month his Father had cleared them out of their home and brought them far away. She'd always wanted to leave the city and live in the country, he'd said, and so Fíli went with him. They owned a small farm and got their meals from their land and the sea, rather than the market places, and there was a sort of peacefulness to it all that he had to admit he liked, though sometimes it was rather dull.

The mer that his Father had struck up an odd relationship with was probably the most exciting thing he'd seen since coming to the village, but he'd never even thought to ask if there were others like him. Thorin had a strange way of talking that was sometimes difficult to understand, his words trilling and clicking even as he spoke in stilted English. Today was no different and Fíli sighed with boredom as he peered out across the still waters, ignoring the way his Father stammered awkwardly through a conversation with Thorin. He didn't begrudge Dwalin his happiness, for Fíli hadn't seen him smile after Mother's death until the day he'd met Thorin, but, couldn't it be just a little bit more interesting?

His wish is granted when a head pops out of the water and his gaze is captured by a pair of big brown eyes, framed in a tan, angular face and dark brunet hair that hung past his shoulders, soaked with seawater. As fast as he sees it, the mer is gone, disappearing beneath the surface to peer at Fíli, looking more curious than frightened or angry.

"Hello," he said slowly, hearing Dwalin and Thorin pause in their conversation to look over at him as he tentatively leans over the edge of the boat to look at the stranger.

"My nephew, Kíli," Thorin explains, sounding fondly exasperated in a way that reminded Fíli of the way his Father introduced him to his friends. 

A smile spread across Fíli's face and he beamed down at the mer, captivated by his bright red mouth and the proud curve of his cheekbones.

"Your name sounds like mine. I'm Fíli, Dwalin's son," he laughed, reaching a hand out towards the water. He felt drawn in by the mer like a moth to a bright light, unable to look away.

Kíli's gaze goes between the hand reaching for the water and Fíli's blue eyes. They're lighter than his Uncle's and he has hair like the metal he finds sometimes in the sunken ships that he's not supposed to go in. Suddenly the race of humans seems much more interesting than it had a few seconds ago. 

Actually just this one, just Fíli. 

The young mer is confused by the outstretched hand though. He waits a moment, hoping for Thorin to give him _some_ kind of hint, but it doesn't come. All Kíli can think is that maybe Fíli wants out of his boat and maybe needs some help? That seems the most likely, although why he doesn't just use those legs humans have to get out is beyond him. 

Besides he wouldn't mind getting closer to this Fíli.

Making up his mind, Kíli grabs the hand outstretched to him and pulls the human out of the boat. He has about a second to enjoy the way Fíli looks in the ocean before an angry blue and black streak is grabbing the human and shoving him back up towards the boat.

The young mer is about to open his mouth to say something when his Uncle rounds on him.

“Humans do not swim or breathe like we do, Kíli!” He growls in their language and pushes his nephew further down into the water, out of reach of the boat and its occupants. “You will kill him doing that!” He leaves the brunet to go back to his post and apologize, as best as he can, for the trouble Kíli's caused.

The young mer is left floating in the water, unsure of what to do, if he should just dive deep enough that Fíli won't be able to see him and wait for his Uncle or something else. He doesn't like the idea of not seeing the human and he probably should apologize. He really didn't mean to try and kill him, that wasn't his intention at all. 

Kíli gives a quick snap of his tail and surfaces near the boat, hearing his Uncle giving a light growl in warning when he starts to get too close. 

“Sorry,” he says after a moment of struggling with the word and not looking at either Dwalin or Fíli.

Fíli had been a little shocked, needless to say, when he'd been suddenly pulled forward into the water, and he didn't even have the time to gasp for air before he plunged into the icy ocean, staring wordlessly at the gleeful face of the mer. Then as quick as it happens, it's over, and Thorin is shoving him back towards his Father's outstretched hands so that he can grab at the edge of the boat, coughing up the water he'd swallowed accidentally. 

He feels bad that the young mer is being punished, though, and he floats there in the water with a hand held tight on the edge of the boat, staring between Thorin's angry face and the sad countenance of Kíli. Dwalin is still inside the boat above him, an uncertain frown on his lips at the tense scene. Fíli doesn't notice this, though. All he cares about is that the happiness has gone from his Kíli's face, and that isn't something he likes.

There's a pressure in his head and a humming like a thousand bees inside his head.

"It's alright. It was my fault. I forgot Father mentioned you don't really understand what shaking hands was. And I'm a good swimmer, really, so it's fine," Fíli attempted to soothe, reaching down into the water to grab his waterlogged boots off and tossing them into the boat. His soaked tunic and trousers join them and Dwalin lays them out so they can dry, leaving Fíli to float in the salt water in his shorts and nothing more. It was actually kind of nice, really, now that the shock of the chill water had worn off.

He offered Kíli a smile and reached out to touch his shoulder shyly, fingers brushing over the surprisingly soft brown hair.

"I've never seen anyone like you before," he admitted softly, missing the amused look Dwalin traded with Thorin now that the scare had passed. 

Kíli's head tilts further and further to the side with each thing that Fíli removes from himself, _clothes_ his Uncle's voice rings in his head. He doesn't understand why humans feel the need to wear them but he likes that Fíli is taking them off. He can see more of him this way and what's not to like about that?

He can also see his legs kicking in the water and that's very interesting to the mer. Where he has fins and a tail to help him swim, Fíli has neither of those and yet here he is actually swimming. It seems like a lot of work though having to kick two legs instead of just a single tail. 

“Saw Uncle,” he says in the human language, wrinkling his nose at the unfamiliarity of it. A few trills and clicks from Thorin have him more aware of what his face is doing; it could be seen as rude, his Uncle says. Kíli gives the human a sheepish smile before returning the gesture though it ends up being less touching of Fíli's shoulder and more fingers gently running through his blond hair.

He can hear his Uncle chuckling fondly and Kíli gives his guardian a pointed glare. He wants to be alone with Fíli, far away from flirting relatives, and the human did say he could swim.

“Good swimmer? Go swimming?” He asks hopefully looking between Fíli and his Father before there's a low sound of disapproval from his Uncle. It's a mix of knowing that Kíli is _very_ good at finding trouble. Actually it follows him around like a shadow if you listen to his mother, and the young mer did almost drown Fíli within ten seconds of meeting him. So, Thorin definitely doesn't think that's a good idea.

Fíli has to think it over as well, staring up at the uncertain look his Father is wearing. On the one hand, Fíli isn't sure how comfortable he is going out into the ocean with only a strange mer between him and floating away into nothing, but on the other hand he is rather keen on spending time with Kíli.

Moreover, this was a chance to get away from his embarrassingly sappy Father and Thorin. That was definitely a plus. 

"I'd like to go swimming with you," he said finally, smiling at Kíli and reaching out to take his hand. After the lecture he assumed Kíli had gotten in that strange language, the mer would remember he needed to breathe every once in a while, hopefully.

"Fíli.." Dwalin began, sounding nervous, and Fíli cut him off with a pointed frown, gesturing around at the water.

"I'll be fine, Pa. Kíli won't let me drown, and we won't go too far. I've finally found someone my own age to be with, so please. I'll be back by the time we head in for dinner, I swear," he sighed, relaxing when Dwalin finally nods in agreement, if a bit hesitantly. 

Fíli grins and turns back to look at Kíli, squeezing his hand tight.

"Go swimming!"

Kíli started to nod along as Fíli spoke before shaking his head and then just looking confused.

“Fíli safe, promise,” he says looking between Dwalin and Thorin, neither of whom look particularly reassured. He was actually a little put out that neither of the two elders trusted him not to accidentally drown Fíli.... a second time.

“I’ll keep him safe, Uncle, I promise. That was just an accident and I won’t let it happen again. I’ll take care of him,” he pleads in their language to a still stern faced Thorin. The other mer looks between Dwalin and his nephew a few times before he lets out a long suffering sigh. 

“You keep his head above the water, Kíli and for the love of the sea keep an eye on him. He says he’s a good swimmer but he can’t swim for too long. They aren’t meant for the water like we are,” Thorin says. The younger mer nods along as he listens very carefully, absorbing each word really and truly for probably the first time in his life. 

“Back by sundown, Kíli,” his Uncle warns, and the threat in his voice isn’t lost on his nephew. Kíli doesn’t doubt that Thorin would ban him from ever seeing Fíli again if his every word isn’t heeded. That’s the last thing he wants but he knows of a little cove where they can go and Fíli can be safe and they can be back quickly if Kíli swims them back.

“Fíli swim little? Kíli watch, Fíli safe.” He smiles at the human and starts to pull on the hand that’s still currently in his towards the land. He considers it a pretty short swim, as he swam a much longer way to get to Dwalin’s boat today, but Thorin had said that humans can’t swim for long. The mer is determined to keep Fíli safe though, and he’ll watch out the entire time to see when the human gets too tired and he’ll swim them the rest of the way. 

Fíli smiles warmly at the mer and nods, loosening his hand from Kíli's so he can sink into the easy front stroke that he'd learned since coming to their new home. There wasn't much swimming to do in London unless you swam in the river, which was generally not advised, so he'd only started to swim recently. He was good at it though, and cut his way easily through the tiny waves that lapped at his body. 

There was little else to do in the village when he wasn't helping his Father fish or tend to their farm, so he'd come to spend a fair amount of time in the ocean and sometimes people even gave him a shilling to watch their children play in the water while they went to the market or tended to their business. It was nice just swimming with Kíli, though, who bobbed and splashed around like a giant dolphin. He'd get flashes of orange and white that must be the mer's tail and he hoped he'd get to see it a little closer. Thorin's was a deep blue color that shone almost beetle black, matching the heavy curtain of black-blue hair that hung around his shoulders. Kíli's had to be just as beautiful, if not more so.

"What is it like, living in the ocean? Do you have a home?" Fíli attempted to ask, stopping his swimming so that he could poorly mime out 'home' to the mer. Hopefully one of them would learn the other's language soon to make talking to each other a bit easier.

Kíli stopped too, head bobbing above the water as he watched Fíli. The young mer isn't sure how to answer his human's first question; he's never really lived anywhere else so he has nothing really to compare it to. Living in the ocean was, well, living in the ocean. How do you explain to someone when you only know bits and pieces of their language?

It takes him a second but he eventually gets what Fíli is trying to motion to him. He nods quickly and points out over the horizon, in the general direction of his home. It's a lot further out than Fíli could ever swim or maybe even possibly make it out to in the little boat Dwalin had and deeper than either could go.

He'd never be able to show Fíli his home and that makes the mer a little sad but he tries not to think about it too much. Dwalin and Thorin have done just fine, so he and Fíli could be fine too.

“Out. With Uncle and Mother,” he says, struggling with last word. He makes sure to keep swimming close enough for Fíli to reach out to in case he got tired.

“Fíli home? With Dwalin and Mother too?” He already knows there is a group of humans that live along the coast, Thorin warned him away from it when Kíli was young, and just assumes that's where Fíli lives with his family. Thorin and Dwalin hadn't technically mated yet, despite their awkward advances, so Kíli could only assume this was because Dwalin already had a mate and that the human simply shared a strange friendship with his Uncle. 

Fíli grows somber at that and shakes his head, offering the young mer a sad smile.

"With Dwalin, yes. My mother died a year ago," he admitted, looking out where Kíli had pointed to the open ocean. It must be nice, being a mer. Did Kíli's kin even know what murder was? 

He can tell he's been quiet for a while by the other's impatient fidgeting, treading water with a distant expression on his face. He hasn't thought about his mother in a while.

"Your Uncle makes my Pa smile again. I haven't seen him smile since she died, not until Thorin brought him a fish one day and told him he was an awful fisherman."

The memory of his Father coming home that night, grinning, made Fíli feel warm despite the chill of the ocean, and he grabs at Kíli's hand again and squeezes, tugging him towards the shore.

"But enough of that. Let's go swimming. We only have a little while to be together before we have to go home, so let us make the most of it."

“Uncle less grumpy too,” Kíli laughs as he leads them to the small cove that he'd been thinking of earlier, swimming close to the human and noticing just how _slowly_ he swam. The young mer thinks that he's definitely swimming them back to the boat or they won't make it back in time. Besides, that means that they can spend longer together before they eventually have to part for the night.

There isn't anywhere in the cove for Fíli to rest but the rocky land, which wasn't really where he wanted them to be. But there is a cave under the water that he and his human can be alone, just in case his Uncle came looking for them early. It was a quiet place and Fíli would be able to sit and rest his legs if he wanted to. 

Although it being underwater brought up a few problems. Fíli couldn't breathe underwater and Kíli had said that he'd keep his human's head above the water. If Thorin did come looking for them he could get in big trouble for taking him into the underwater cave, but at the same time they couldn't really stay in the cove. So, he could possibly argue that he was just trying to take care of his human.

He gives Fíli an uncertain look.

“Fíli, go under? Hold Kíli, swim fast. Fíli go,” he makes an over exaggerated gasping noise before covering his gills. He knows that whales and dolphins can hold their breath when they go underwater and they breathed the air as Fíli did. So Fíli should be able to do the same, right?

Fíli stared at Kíli for a long moment before he made the connection, beaming at him and nodding.

"Fíli go under," he agreed, sliding through the water so he could wrap his arms around Kíli's chest from behind, trying not to shiver at how nice it felt to be pressed up against the mer this way. It was as if a beautiful song was filling him up from the inside at the contact. Music he'd only ever heard in his dreams before now. 

He buried his face in the tangled web of brown hair in front of him, breathing in the salty scent of the ocean that clung to it.

"Fíli go under with Kíli."

He closed his eyes and took a deep breath.

Kíli smiles wide when he feels Fíli's arms go around his chest and is glad that his human is behind him so he can't see. The smile is probably just as sappy as the one that Thorin gets when he's even _thinking_ about Dwalin.

He places one of his arms over Fíli's and dives straight down, easily finding the entrance to the cave. Now comes the part where he really needs to swim fast, the tunnel to the cave is nothing for Kíli but he's also not the one holding his breath. He swims as quickly as his tail will carry them, his eyes adjusting to the darkness and allowing him to easily navigate the bends that take them deeper into the water before going back up.

The young mer heads straight for the surface of the water once they clear they entrance, making sure to get his human some air before he drowns.

“Sorry. Fíli, okay?” He turns his head trying to get a look and realizes just how closely that brings their faces together. For a moment, he's tempted to nuzzle against the wet hair but decides letting Fíli rest and catch his breath is probably more important right now. 

He swims to a boulder in the middle of the cave that's lit by the sun coming through cracks in the ceiling. It's flat enough and big enough to lay on but usually Kíli stays away from the rock unless he wants to nap. It's hard to see the things that glow blue on the ceiling when you're sitting on the boulder, and he really likes those.

At first Fíli's too busy trying to gulp down air to notice much else, his lungs aching from holding his breath for so long. But when Fíli hauls himself up onto the boulder and really takes a look around, his jaw nearly drops off his body.

They're in an underwater cave, filled with shiny spires of stone that drip and echo in the expansive cavern. It'd be dark, besides the one spot of light, if it wasn't for the thousands upon thousands of strange, glowing tendrils that hang from every single surface he could find. The eerie blue light shines on Kíli's excited face, and if possible makes him even more beautiful to the fisherman's son.

"Kíli this is.. this is amazing! What on earth are they?" he asked in a soft gasp, reaching out to rest his hand on the mer's shoulder as he speaks. He likes to be touching him, now, after having been in contact just then. Touching Kíli feels right. 

Fíli sweeps his soaked blond hair behind his ears and looks up at the cavern ceiling, seeing the cracks in the rock where light and air managed to get inside. 

"It's so beautiful. Thank you for showing me this, Kíli."

He looks back down at the mer and smiles softly, eyes crinkling faintly with happiness. He doesn't remember the last time he felt so content.

Kíli shrugs before he drags himself out of the water too, laying out on his back next to Fíli. He keeps some of his orange and black tail in the water, letting it lazily flick back forth and causing the usually still waters to ripple. 

“Glowing things,” he says honestly, folding his arms behind his head. He's only seen them in a few other caves besides this one and really has no idea what they are. They're always too far out of his reach and just stay up there and glow. They never move that he's seen so he thinks they must be a plant because animals definitely can't hold still for that long. 

They don't hold his attention for long with Fíli next to him though. Between the blue of the light and the sun catching his wet hair, his human looks better than anything in here, or anything that the mer has ever seen. He still thinks Fíli's legs and the clothes he has around them around them are weird, but not in a bad way. Kíli thinks that he's even starting to really like them the longer they stay together, and isn't that something. Just this morning he wanted nothing to do with anyone with legs but now all he wanted to do was spend every second with this human.

“Welcome,” he replies softly. 

Fíli's eyes go wide when Kíli's tail comes into view, staring awestruck at the rippling orange, black, and white scales. He'd never seen a fish like this before and it made him think of bright things and warm sunshine and faraway places he's only ever read of in books. 

"You're amazing, Kíli," he breathed, reaching out to touch before hesitating, gaze flitting up to meet the young mer's.

"Can I look at you? Only, you're the most beautiful thing I've ever seen in my life, and I'd really like to touch, if you don't mind."

It felt like such an intimate question, asking Kíli if he could touch his tail. He'd never really seen his Father touch Thorin's even, except for the few odd times the mer would consent to joining them in the boat. Of course that wasn't to say they weren't doing things when he wasn't there, but Fíli didn't really want to think about his Father having sex or doing any sort of... touching.

"I promise I'll be gentle," he whispered softly, enraptured by the way the light of the glowing strands made the scales shimmer and move like liquid.

If the question felt intimate to Fíli, it probably was because for a mer, it _is_ an intimate question. Tails are very important to mer with touching being reserved for family, close friends, and mates. Mer that usually the one in question trusted. A serious enough injury could cause their tail to become useless and it was thought kinder to kill a mer than take the use of their tail.

Even knowing all that, and fully aware that he barely knows anything about his human, the young mer still nods. Fíli had trusted him not to kill him when he'd brought him through the tunnel so he thinks he can allow this.

Besides he _wants_ the other to touch him, to maybe be his mate one day. No one outside of his family has ever touched his tail and he suddenly wants Fíli to the first and only.

Kíli raises the rest of himself out of the water, letting his human see all of him. He nervously watches his face, because the mer isn't colored like the rest of the mer around here, and he isn't used to being called beautiful. His mother says that he's colored like some fish in the warm waters where his Father is off exploring, brave little fish that can be among the poisonous arms of things that grow there.

Fascinated, Fíli lets his fingers brush carefully along the ridge of a brilliant orange scale, shivering at the strange, cool feel of it, biting at his lower lip as he explores. They're hard, as he expected, but don't feel as smooth as they look, but more similar to the roughness of a cat's tongue, catching slightly on his fingertips. 

"It's amazing. You're amazing, Kíli," he murmured, shifting onto his knees so he can run his hand over one of the many fins that the mer has, feeling the spines that run through the webbing that give Kíli control over their movement through the water. He hardly notices the effect his touching has on the other, so enraptured is he in the strange beauty of the mer's body. 

Fíli rests his palm flat against Kíli's side and rubs it slowly down his body towards fin furled out where his knees would be, if he had legs, shivering at how it feels against his skin. If it felt this nice on his hand, how would it feel elsewhere? 

And suddenly Fíli doesn't really notice the chill of the air against his damp skin anymore.

Kíli doesn't notice much outside how amazing Fíli's touch feels, how warm it makes him feel all over. He fights to keep himself from moving into the touches too much because there is no way that Fíli knows that the underside of his fins are particularly sensitive. He also can't know that those kinds of touches are saved for mates only.

The human couldn't know that right? What if he did, though? What if Thorin had said something to Dwalin, who told Fíli? That wasn't so farfetched was it? His beautiful human could be doing all of this on purpose, wanting to be Kíli's mate even after such a short time.

The young mer was okay with that. Actually he'd be much more than okay with having Fíli as a mate, right now if possible. He wants to push up and roll the human on his back and crash their mouths together, but there's still a little part of him that doubts Fíli knows what's he doing to the mer.

Kíli stays laying against the rock, trying to figure out if his human actually knows or not, becoming more and more content just to stay still and let Fíli touch where ever he wanted so long as he didn't stop touching. 

He can't stop the way his fins tense though when his human runs his fingers along the underside of the fin on his other side.

Fíli's hand jerks away the second Kíli's muscles ripple and tense, looking worried when he finds the mer's gaze with his own.

"Did I hurt you? I'm sorry, I didn't mean to. Do you want me to stop?" he asked softly, even as his mind cried out in protest at the idea of no longer touching him. It felt right to touch him like that, and to brush his knuckles along the delicate seeming webbing of Kíli's fins. 

He doesn't want to cause his mer - his mer? - any pain, however, and forces his hands down onto the stone, cheeks flushing slightly with embarrassment. He must have gotten carried away and found a sore spot on Kíli, or been too familiar. After all, he had only just met Thorin's nephew, and he was basically pawing and rubbing at his thighs for all intents and purposes.

The buzzing song in his mind grows louder.

"I'm sorry, Kíli."

“No sorry. Not hurt,” the mer says quickly and pushes himself up so that he can lean back on his hands. Now that the touching has stopped though and he can actually think straight, he can't find it in himself to admit that Fíli's touch felt good or that he never wanted it to stop.

The way the human reacted is also enough for Kíli to know that he really didn't know what he was doing. Which makes him feel like an idiot for assuming that Fíli would want to be his mate in the first place. They barely know each other so there's good reason for the human to not want him for a mate.

He leans forward over his tail, letting his drying brown hair hide his face from Fíli as he cups a little bit of water to pour over himself. He's going to have to explain why he reacted like he did sooner or later. Maybe if he's lucky Fíli won't hate him or tell Dwalin and Thorin.

“Touch not hurt. Touch good,” he admits in a small voice, scooping up more water.

“Good touch only for mate. Uncle says.”

Fíli stares at Kíli for a long moment, digesting that. If the touch was good, then why had he flinched?

And then the pieces fall into place and his mouth drops open once more, a blush spreading clear to the tips of his ears.

"Oh God, I am so sorry, I never meant to impose like that, truly. Please apologize to your mate for me, I didn't know," he says in a rush, trying to ignore the ugly jealousy that wells inside him at the idea of another touching Kíli like that. He's being unfair, of course. He's known the mer for all of two hours, but he can't help the dark possessiveness he feels already.

The singing in his head grows deafening.

Fíli leans down to dunk his head in the water, taking a long moment to try and settle himself before reemerging once more, hair hanging wetly around his shoulders. The cold shock seems to center him, though, and he smiles faintly at Kíli, cupping some of the water in hand to help him dampen the scales of his tail.

"Your mate is lucky to have a creature as beautiful and bewitching as you," he murmured softly, unable to resist one last brush of a fingertip over the edging of his tail fin. 

Kíli can't help the little bit of nervous laughter that escapes him before he clamps his hand over his mouth. He can only imagine that his mother would have burst out into a laughing fit if she heard what Fíli said. She was always going on about her son being too adventurous for a mate or still acted too much like a youngling for one. With all the mer he's met in his life, he was fine with not finding a mate, besides he was still young.

Although no one ever counted on him finding a human interesting enough to want to be mated to.

“Kíli, no mate,” he shakes his head and gives Fíli a sheepish smile. He can see the confusion all over the human's face and makes a mental note to have his Uncle teach him more of their language. 

That puts them back at square one, but the mer doesn't hide his face this time, though he's still just as worried about Fíli's reaction.

“Fíli touch good. Very good,” he tries to explain, drawing out the last two words, “very good touch only for mate.” 

Kíli nods as he speaks, trying to will Fíli to understand. The one time he feels like things would be easier if Thorin were around is also the one time the young mer is so glad that his Uncle is nowhere near them.

Fíli is hesitant at first, unwilling to repeat his past faux pas, but very carefully cups his palm against the flat of Kíli's dorsal fin, letting it brush down the rippled side like one would pet an animal.

"You like it? You.. want me to keep touching?" he asked slowly, a pleasant heat settling in the pit of his belly at this. Good touch reserved only for mate. His mate, his mer.

The singing in his mind pitched with energy as he scraped his fingernails lightly against the crease where fin met scales, shifting slightly to try to press his knees together. He wished he'd at least kept his trousers on, now, for the damp cloth of his shorts left little to the imagination in a situation like this.

"I like it, too. I like touching you," he whispered, mesmerized by the dance of light on Kíli's scales and the song in his head as he brushed his palm from the mer's belly down to where his kneecaps would have been.

"I like touching you like a mate."

Kíli nods quickly and doesn’t even bother trying to stop his body from arching into the light scratching along the base of his fin. It’s something he wasn’t even aware that he’d like, and part of it is just because it’s Fíli touching him, he's pretty sure.

The mer wants more though, pushing himself along the rock to get close to the human. He touches the bend in Fíli’s legs with gentle fingers, and he doesn’t know if his legs are sensitive like his own fins are but he really wants to find out. He also wants to see what’s under the last piece of cloth that Fíli has yet to take off.

“Kíli touch Fíli?” He asks when he realizes that he never asked for permission like Fíli had. He nuzzles against the human’s cheek like he wanted to earlier, liking the smell of sunshine and ocean breeze. 

There’s another question the mer has on his mind and it’s one that he’s much more nervous about. He thinks Fíli understands what their touching means now but he wants to be absolutely sure. 

“Fíli… Kíli’s mate?” 

Some sensible part of Fíli's brain is screaming that this is wrong and that he barely knows Kíli, and his Father would be furious.

It's drowned out by the music in his head, the beautiful singing that filled him up the second he laid eyes on his mer, that drove him this far and kept him here beyond all doubt and uncertainty.

"Fíli is Kíli's mate.. and Kíli is Fíli's mate?" he asked softly, shivering when the brunet's webbed hand brushes over his knee, Kíli's mouth dangerously close to his own. He avoids it for now, though, much more interested in the delicate folds of gills lining his mer's throat. He brushes his lips across them with a shuddering sigh, tongue darting out to tease at the foreign flesh. 

He'd been intimate with people in the past before, admittedly, though, all but one had been female. None had ever been so fascinating, or as responsive, as Kíli, though. 

Kíli tasted like the ocean, unsurprisingly, but it was a clean sort of taste, rather than salty or unpleasant, and Fíli pressed further into the contact, lapping at the ridge of the mer's gills with intent little noises. At some point he'd ended up flush against Kíli's side, but the proximity seemed to quiet the intensity of the song in his mind and so he made no move to give them space, instead taking the other's hand and guiding it higher up his body, to the spot between his legs where he ached for contact.

"Kíli touch Fíli."

“Yes. Fíli's,” the mer gasps, tilting his head to give his mate better access to his very sensitive gills, whimpering as his eyes flutter shut. 

_His_ mate. _His_ Fíli. The words make him both giddy and possessive, wanting to leave claiming marks along his shoulders and gill-less neck. The only thing holding him back is that Thorin and Dwalin would see once they got back to the boat. While he'd never deny that Fíli was his, and he was Fíli's, he has a feeling that they're going to be in trouble for committing to each other so soon.

The mer couldn't care less at the moment though, he has his Fíli next to him and that's all that matters.

Kíli's hand is gentle as he runs it over the spot where his hand was led. There's a hardness that wasn't there before, or at least he's sure wasn't there before, and he likes all the little noises that Fíli makes when presses just a little harder. He doesn't really like the feeling of the clothes though, it feels strange under his hand and he wants to touch more skin.

The first thought he has is just to rip the thing off with his nails but then they would have to explain to Thorin and Dwalin what happened. He paws at the material instead, whining when they don't come off.

“Off? Please? Kíli touch more,” he begs.

Fíli actually blushes when Kíli asks him to remove his shorts, shuddering as he moves his hands from rubbing at the mer's fins to tug the material down and off, leaving himself bared to the mer's attentions.

He's already hard, cock jutting out from a bed of wiry golden hair and flush with blood, and the sight of it gives Fíli pause, gaze flitting up towards the brown haired man.

"Do you have anything like this, Kíli? Somewhere I can touch you that feels really good?" he asked, reaching out to grip at the fin flared along Kíli's side, rubbing his thumb into the sensitive webbing. He knew the basics of how sex between two men worked, but, then, Kíli wasn't exactly a man in the human sense. Did mer even have the same anatomy?

He swallowed thickly and leaned in to blow hot air across Kíli's quivering gills, tongue darting out to tease the delicate seam.

"How do mer mate, Kíli? I want to be your mate."

Kíli nods absently as he studies the unfamiliar body before him, committing the details to memory. While he doesn't have the exact same thing as Fíli, he does have something that's at least similar and he knows it would feel good if Fíli touched him there.

He doesn't know how to really explain it though, not in a way that his mate would understand. Where Fíli had guided his hand to a place that felt good, Kíli didn't really use his hands for touching such things. Actually no mer did. 

Trying to explain that though makes him feel like he did when he was a youngling and had to watch as his Uncle failed miserably at explaining how things worked between two mer to him. 

“Kíli show?” He asks but he's already nudging his mate to lay back on the rock.

“Kíli no use hands. Kíli move,” he pants against the skin of Fíli's neck, grinding against him just once to show him what he means.

Fíli's surprised when Kíli's laying him back against the rock, but, the surprise morphs into something much better when the mer is moving between his knees and something slick grinds against his hip. What looks pretty similar to a human cock has slipped out of Kíli's body from a puckered slit roughly where his groin would be if he had legs, and Fíli can't help but stare at it for a long moment, mouth open. It's tapered and thinner than Fíli's own, but other than that it's roughly close enough that he can at least make a guess as to how it works.

"Fíli likes it when Kíli moves. Feels very good," he groaned, shuddering at the rough friction of the mer's scales against his cock combined with the wet slide of Kíli's own length, the blond's legs parted wide around his body. He starts to sweat, despite the chill of the air, and he clings to Kíli as they move together, mouthing his way across his cheek to crash their lips together, tasting his mate for the first time.

Like his skin, Kíli's tongue tastes like the ocean air and it leaves Fíli breathless with unfamiliar memories of diving through the waves after fish and chasing seagulls high above him. 

And Fíli longs for a place he has never known. 

Kíli sees the same images flash through his own mind as he uses his tongue to map the inside of his mate's mouth. Fíli tastes a little like the water he must have swallowed when the mer pulled him out of the boat but there are other things too that he doesn't know. He also notices that his teeth are blunt where Kíli's are more pointed for biting into fish, which makes him all the more careful when he nips at his mate's lower lip. 

The mer has to support himself on his elbows to give himself enough leverage to keep grinding down against Fíli. He can't help but think that this would all be easier in the water but he can't risk accidentally drowning his mate.

He likes the way his human moves under him though, along with the smoothness of his skin combined with the slight scratch from the hair he has.

“Fíli,” he whimpers as his body starts to feel warmer and like it's too tight. He slips his tongue back inside his mate's mouth, trying to envision the cave he calls home, wondering if he can control what Fíli sees. It's a good distraction from the need to bite and claim the human as his.

Fíli groans into the kiss as pleasure shoots up his spine, one hand buried in the mer's dark hair while the other is leaving red lines down his back, fingernails buried in the dark tanned skin. It's overwhelming and yet not enough all at once, Kíli grinding against him like this, and the flashes of memories that don't belong to him are dizzying, combined with the pitching cries of music.

"Mate, my mate. Kíli. Want you inside me, want you to mate with me," he whispers in a jumble of words, thrusting his cock up against the mer's before gripping his shoulders and rolling them over. It'd probably be easier with the water to slick the way, so Fíli slips off the edge of the rock once more and rests an arm on it to keep his head above the water, his free hand sinking behind him to rub at the pucker of his entrance. The chill ocean helps numb the discomfort a little when he presses a finger inside, though it is admittedly not the best of lubricants. But seeing as their options included glowing ceiling strings, sand, and water, Fíli was gonna go ahead and stick with the water. The voice crooning to him in his mind left no room for argument that he needed Kíli inside him. It would mark him as the mer's mate, as _Kíli's._

Fíli didn't really understand how he knew this, but, he also didn't care.

Kíli watches him dumbly for a moment, while his mind works to catch up with what just happened and what his Fíli is doing now. He can't see where his hand goes while he's still on the rock, so he rolls off the opposite side and swims around to get a better look. Where he thought maybe there would be a slit like he himself has, there's just two round globes at the top of his legs. 

The mer takes one in each hand, noting that he very much likes the way they fit in his hands, so that he can spread them and get a better look at just what his mate is doing to himself. There isn't a slit like he thought, just a hole that Fíli's finger is currently inside. 

He slips the digit out to replace it with his own, letting out a low growl at the tight heat that envelopes his finger. 

It might be too tight and when he looks up to the surface he can the slight discomfort on his mate's face. Without even thinking about it, he moves forward enough that he run his tongue over the puckered skin around his finger, like he would do if he was injured.

Fíli's reaction though has him breaching the surface of the water and nuzzling against his cheek.

“Mate hurt? Kíli sorry!”

If Fíli's surprised by Kíli's finger nudging his own out of the way to take its place, he's absolutely shocked when what is undeniably the mer's tongue is sweeping across the sensitive flesh, hips jerking forward and a strangled cry torn from his throat. He regrets his reaction when it makes Kíli stop, though, gasping wetly and staring at him as if he'd grown another head.

"Oh God, no, mate not hurt. Mate good, mate very good, Kíli," he whispered, gripping the edge of the rock so tight his knuckles blanched. He hadn't been taken since the one time he'd lain with another man, and he'd expected it to be mostly uncomfortable, as it'd been then, too. But, if Kíli kept doing _that_ then perhaps it wouldn't be so bad after all.

Fíli offered him a breathless smile, sliding a hand behind himself once more to work a finger into his body, curling it to rub at the muscle until it loosened up.

"It felt good, my mate. Please do it again?"

Kíli gives him a mischievous grin before he sinks back into the water. He had found somewhere else that his mate liked to be touched, just like Fíli had seemed to so easily find all of his own sensitive areas. And if his human liked it, then the mer was more than happy to oblige.

He sinks down until where the finger is working is right at his eye level and uses his smaller fins to keep him stationary, occasionally brushing against his mate's legs. Kíli uses his hands to spreads the round globes again, but leaves Fíli's finger where it is as he starts to lick around it. 

The mer watches and listens for any more signs of discomfort but the noises his mate is making are like the ones he had been making before and they're an intoxicating thing to listen to. Kíli becomes greedy for more of the sounds, to know that _he_ is the only one that can make Fíli feel so good. He carefully brushes his human's hand away again before pressing a kiss to the skin and sliding his tongue inside where he'd used his finger before. He copies the way the digit had been moving, thrusting his tongue in and out and dragging it along the ring.

Fíli shudders at the heated swipe of Kíli's tongue against his entrance, struggling to keep his finger moving inside him to prepare himself for what was to come. No one has ever done something like this before, and the sheer filthiness of Kíli's tongue there is deliciously erotic, Fíli's hips rocking of their own accord with every lick and probe of the warm muscle. 

But even that doesn't prepare him fully for how it feels to actually have the mer _inside_ him, gripping onto the edge of the rock with both hands to keep from sliding down into the water as pleasure blooms in his belly. Kíli's tongue is thrusting inside him, licking at his inner walls and tugging at the ring, dragging stuttered wails from the human with every single touch. It doesn't help Fíli's sanity, either, that Kíli's tongue is rough like his scales, creating a pleasant friction against the sensitive hole with every stab into him. 

"Oh Kíli.. My Kíli.. Please, I can't, I'm gonna come," he choked out, the muscles in his thighs twitching and jumping as he fought down the orgasm threatening to rise up inside him. He didn't want to come just yet. He wanted to come with his mate buried in his body.

"Need at least one more finger, Kee, before I can take you."

He doesn't know where the nickname comes from, but he likes the sound of it as he slipped his hand back again, working two digits into his body as quickly as he can without hurting himself.

Kíli smiles at the nickname as he surfaces and nuzzles into his mate's neck, letting Fíli continue what he's doing with his own fingers. He wanted to continue to use his tongue and drag more sounds out of him, but he also wants to mate with his human sooner rather than later.

“My Fee,” he murmurs happily against the human's ear, lightly running his tongue along the shell. He wraps an arm around his mate's chest, pulling them together, and placing the other arm on top of the rock to help hold them both up. Well mostly Fíli, since it wouldn't be a problem for the mer to slip under the water.

“My mate,” he growls lightly as he drags his teeth down from his ear, along his bare neck and shoulder. He nips lightly at the tan skin, not nearly enough to leave the deep bruises that he desires, but the fading marks will have to do. He contents himself with them, deciding that later, once their guardians know, and if Fíli is okay with it, he can do it properly.

“Fee, need,” he whimpers, grinding his cock against the one of the swells at the top of his mate's legs.

Fíli muffled a moan as Kíli ground against his ass, fingers stuttering inside him. He knows he's going to regret this tonight, when he's aching all over and unable to move from his bed, but, right now the singing is telling him that he cannot wait any longer.

He slips his fingers out from inside him and hauls the arm up onto the rock to steady himself further, spreading his legs so that Kíli will get the point.

"Inside me, my mate.. Inside where my fingers were," he croaked softly, head tossed back on the mer's shoulder and flush against his chest. 

This was insanity. He'd known the creature for a few hours at the most and here he was, all but presenting for him, asking to be taken and mated like an animal. And yet, he couldn't really bring himself to care in that moment. When Kíli pressed inside him, blessedly going slow to rock in a little bit at a time, the singing became softer, gentler, and warmer, filling the human up with a pleasant happiness he hadn't known since before his mother's murder. 

He was hearing Kíli's song. The song of his mate.

Besides the _warmth_ and the _tightness_ of Fíli's body wrapped around him, Kíli notices the sense of right and wholeness as he hasn't know before. He never felt like anything was missing from his life before but now that he has his mate, he can't imagine ever being without him again. How was he supposed to part ways with him later tonight?

He banishes that thought because they're both here now, and that's what was important. He just wished that he knew the words in the human language to express what he felt to Fíli.

The mer continues his slow motions, not wanting to hurt his mate and unsure if he's supposed to feel so tight, until he's eventually seated completely inside. Kíli can feel the way the muscles flutter and eventually start to relax around him. He waits, kissing every inch of skin that he can reach before eventually finding Fíli's lips again until he feels like his mate is relaxed enough to give short thrust.

“Fíli okay?” He asks, waiting for affirmation before he gives a slow roll of his tail.

Fíli is more than okay. He's overwhelmed with sensation as Kíli settles deep inside him, feeling the heat of his cock in his body and the friction of scales against his skin, and the steady pressure of his mate's arms around his middle. He feels like he could soar, his nerves alive with energy and mind crying out the song he'd come to know more intimately than his own reflection.

"Fíli's okay," he whispers, loud and echoing in the great cavern. He sinks into Kíli's kiss with a ragged little moan, reaching behind himself to bury a hand in the mer's hair, shaking as he tries to keep from coming on the spot.

Not breaking the filthy kiss and with his tongue tangled against his mate's, Fíli begins to rock himself backwards on Kíli's cock, as best as he can in the water. He wondered what it would be like to be taken completely under water, to be surrounded in the cool ocean while his mate twined against him and around him.

Fíli had never wanted to be someone else so much in his entire life as he did in that moment.

Kíli matches his rhythm easily to his mate's, rolling his body forward as Fíli rocks back. He wraps the end of his tail around of his mate's legs, letting his fins brush against the appendages, while he keeps a hold of Fíli with his arms. Even though they're about as physically close as they're ever going to get, he wants to be closer still. 

The mer can feel the way his body shakes against and around his own, making him moan into his mate's mouth. He moves faster as the pitch in Fíli's voice changes and as his own need to come barrels forward as well. All of these new sensations are the best things that he's ever known and it feels like it's going to end far too soon for his liking.

“Kíli, Fíli's,” he says quickly before devouring his mate's mouth again. It's the only way he knows how to put words to the emotions he feels.

“Mine,” he says, punctuating with a particularly sharp thrust of his tail.

Fíli's incoherent by this point and nodding desperately to what Kíli's saying, gasping wetly into the mer's mouth as the water roils around them with their movements, sending splashes up his back that cool his heated skin. Sex had never been this intense for the blond before and he whimpers as Kíli fucks into him again and again, his body easily accommodating his mate. 

A pleasant ache has begun to spread through him and Fíli relishes it, tugging on Kíli's thick hair to smash their mouths together again, no longer caring about breathing or anything else except the mer. He can feel Kíli inside him, hot and long and fucking into him impossibly fast, now, and Fíli doesn't try to stifle the screams tearing their way from his throat, locked in the curled embrace of the brunet's tail. 

Then he decides to let go of the rock and takes a deep breath before they sink down into the water, making him shudder as the chill ocean envelops him. It feels good, though, maybe even better this way, and Fíli rocks himself back against his mate, inviting him to completely let loose. 

Kíli is worried at first, thinking maybe that Fíli's hand had slipped from the rock and was starting to untangle his tail to get back to the surface when his mate pushes back against him. He's still worried but a little less so, using the fins at his sides to keep them just below the surface of the water. He loosens his hold a little on both the legs that his tail is wrapped around and the arms around his chest, just in case his mate needs to push him away so he can breathe. 

And then the mer starts fucking into Fíli with reckless abandon. He's aware that his time is limited because of his mate, but there's also a tell-tale warmth starting to coil in his gut. 

He tries to tell him as much but being underneath the water and so thoroughly caught up in Fíli, all he can do is make desperate noises in his own language. Kíli isn't even aware that his mate doesn't understand a thing he's saying as he nips along the cord in his neck.

And while Fíli may not be able to understand what Kíli is saying, the message is clear enough as they twist and roll beneath the surface of the water, the human completely at the mercy of the ocean dweller. His lungs burn with the need for oxygen, but he ignores it as pleasure washes over him, knowing he can last just a little bit longer.

Kíli's chattering in his ear in that soft clicking hum of his own language and he exhales a stream of bubbles, body tightening around the flesh spearing into his core again and again. When he can take it no longer he finally pushes himself up enough to get his head out of the water, gasping for air even as Kíli's cock finds the spot inside him that has him seeing stars.

Or perhaps that's just the glowing strings on the ceiling.

"K-Kíli! Kíli!" he screams, fingernails scrabbling at the arms around his middle as the pleasure peaks within him and then crashes down like a tidal wave, clouding the water with his release as his body twists and writhes. The rush of oxygen to his starved lungs only heightens the moment and the singing in his mind pitches and then washes over him like a gentle tide, ebbing away with the intensity of his pleasure until it's little more than a comfortable, soft melody in the back of his mind. 

Kíli comes when he feels Fíli's body pulsing around his cock, a low growl escaping him as he marks his mate's insides. The mer is quick to untangle his tail from around his leg, floating them along the surface and letting Fíli rest against him as he lazily glides through the cave while they both recover. They stop for only a second so that the mer can slip out of his mate. He doesn't move his arms from around the human's middle though, unwilling to completely unwrap from Fíli.

He hums a tune softly as they move, letting his fingers explore where they hadn't before. There's hair on Fíli's chest that he likes to run his fingers through and just a little bit on his lower stomach that seems to lead further down. He likes running his fingers over that as well. There are muscles that jump and twitch as he moves his hand and the mer notice that they're pretty much the same as far as top halves go. 

What Kíli really likes though are the things that are below. Like the globes at the tops of Fíli's legs and the smooth feel of them against his tail. He's quick to slip a hand between them and palm over one as he nuzzles against his mate's head.

Fíli has never felt so relaxed in his entire life, laid back against the mer and drifting gently through the water. Ever since coming to their new home, he's loved to swim, but now he had a feeling he'd enjoy the ocean for entirely different reasons.

The content moment is broken when Kíli's exploring fingers curl around his ass, squeezing and rubbing with fascinated intent. It draws an amused laugh from the fisherman, who grins over his shoulder at his mate.

"What is it with you creatures and rear ends? Your Uncle is embarrassingly obsessed with Father's, too," he snorted, reaching up behind him to lazily massage his fingers against Kíli's scalp. The cold water helps to numb some of the discomfort he knows is headed his way and he couldn't be more thankful, turning his head so that he can nuzzle against the sensitive gills lining his mer's throat.

He closes his eyes and tries to memorize this moment, holding on to the gentle singing in his mind and the feeling of his mate's arms around his middle, the faint scrub of scales against his thighs, and the smell of the ocean clinging to the air. 

"I can hear you in my head. Your voice. It's singing to me," he murmured softly, pressing a kiss to the edge of his gills and smiling against the delicate skin.

“Kíli tail. Fíli no tail. Kíli touch,” the mer tries to explain, squeezing the globe in his hand again. Actually, he thinks that even if he were human he'd like playing with Fíli's – rear end? - roundness. The way it fits into his palm like it was made for him is fantastic. 

Although knowing that his Uncle was obsessed with Dwalin's was probably a little more information than Kíli ever needed to know. He's happy to just keep believing that all that ever happens between the older pair is that Thorin helps him fish.

He hums happily as fingers find his scalp and his mate's lips find his gills. The mer wants to stay in this moment forever, lazily swimming around the cave with his Fíli, occasionally mating and learning where else he likes to be touched. He doesn't think about how they'll have to leave to meet up with their guardians and go their separate ways at least for the night.

“Kíli's song for mate. Fíli Kíli's mate,” he grins. Even if there had been a doubt before, there definitely isn't now, knowing that Fíli hears his song. It's also a useful thing to know for when they eventually tell Dwalin and Thorin, and Kíli's mother, about their relationship.

Fíli hums thoughtfully at this, fingers tracing vague shapes into Kíli's hair. 

"Your song for mate... so like, your siren song?" he asked in a low voice, looking up at his mate. He supposed not exactly like a siren song. For one thing, Kíli hadn't eaten him, which was a huge plus, and for another, the mer seemed surprised that Fíli could hear his song. 

Either way, it was kind of nice, this soft melody in his mind. He wondered if it would still be there when they were apart. He found himself hoping it would be, for it'd be a small reminder that he wasn't so alone anymore, and that somewhere out in the water his mate was waiting for him.

The thought made him smile and Fíli leaned up to kiss the mer, turning in his grasp until they were facing, arms slipping around his shoulders so he stayed afloat without having to kick.

"Your song is very nice. I like hearing it," he chuckled, fingers brushing over the webbed spines of Kíli's ear. Everything about the mer was so strange and fascinating, so different from his own body. He could see why he was so enraptured with Fíli's ass, now, besides the fact that it was a pretty great one. 

“Siren?” Kíli asks after fumbling over the word. He doesn’t know what that means but the way Fíli is looking at him makes him think that it might not be a good thing. Maybe Dwalin had told his son about the humans that ran their boats aground trying to get to the mer that were hiding among the rocks.

Which really, some of those boats the humans had were bigger than some whales and usually full of other humans. Who could really blame the mer for trying to hide from them? Humans had nets and usually nets were bad for his people.

He grins as he tries to brush away his mate’s hand from his ear, the touch tickling against the webbed skin.

“Kíli like Fíli,” the mer says, reaching for another kiss. He continues to lazily swim them around the cave, running gentle hands over his mate’s body, committing every detail to memory. If a hand happened to stray down to his _rear end_ , he didn’t think he could be blamed for that.

Eventually Kíli lets out a slow, high, whine, sensing that the sun is getting low in the sky without even having to look to the crack in the ceiling of the cave. They’ll have to head back soon and right now that is the absolute last thing that he wants right now or ever. 

“Go soon,” he pouts. 

Fíli chuckles low in his throat, eyes creaking open to blink at the unhappy creature.

"But I'll be back. I'll come whenever Father visits Thorin, and we can come back here. It'll be our cave, our special secret," he said quietly, nipping a line along his jaw before finding his lips in a kiss. It was probably for the best that they returned soon, for Fíli was starting to feel chilled from the ocean water and only the blazing heat of the mer against him kept him from shivering. 

He grabs his shorts from the rock when they circle back by it and tugs them on, as unhappy as Kíli is at the prospect of being parted, no matter the cold. His mind was insisting that this was his mate, and they had to be together, and that to be parted would be the worst misery.

"It's no wonder that my Father is always eager to rush back out here. Knowing that I'm about to leave you, and not see you for a while, is quite possibly the worst feeling I've ever known," he admitted softly, fingers brushing through the mer's tangled brown hair.

Next time he'd come earlier and stay longer. He'd ensure each visit lasted, so that he could make it to the next one, and the next one. 

Kíli wrinkles his nose at the thing that Fíli puts back on. He doesn't understand why humans feel the need to wear such things, but those particular clothes signal the end of their time together today. So, those clothes are extra annoying to the young mer and they don't feel as nice against his tail as his mate's skin had.

“Kíli come with Uncle. See Fíli,” he mumbles. He tries to remember that they're just parting for the night and not forever. As soon as he can get Thorin up and out of their home tomorrow, he can see his mate again and everything will be fine. Assuming of course his mother or Thorin didn't string up by his gills for making a human his mate after barely knowing him for a few hours.

They could have all day tomorrow instead of just a few hours though, and that's enough to make him at least partially alright with taking Fíli back to his Father. How he wishes they could stay though.

The mer slowly guides them to where he knows the entrance to the cave is, taking as long as he can to get there while he kisses and squeezes Fíli against him.

“Go,” he does his exaggerated gasping noise again as he turns them both upright in the water. He steals one last kiss before Fíli holds his breath and swims as fast as he can out of the cave and to the surface on the other side.

Fíli squints in the fading sunlight when they emerge outside the cave, arms still tight around his mer's shoulders. Everything seemed so loud and open after the quiet darkness of their cave and it signaled the end of their time together.

Only for a little while, though. He'd see Kíli again tomorrow and they'd be together for even longer. He wanted to get to know the creature he'd taken as his own. He wanted to know what Kíli liked to do, and the things he'd seen and experienced, and all the memories he had. Fíli was sure that he had quite the story to tell.

So rather than being sad, he smiled at the brunet and brushed his fingers through his hair, trailing against the webbed arch of his ear. 

"Can I draw you tomorrow?" he asked softly as the mer swam them back towards the distant black dot of the boat, chin resting on his shoulder. He'd have to find a way to wrap his sketchpad up so it'd survive the water. Maybe they could find the sandbar near the lighthouse and Fíli could draw the way the sun made Kíli's scales glimmer like fire.

Kíli lets out an involuntary giggle as Fíli's fingers brush against his ear, gently batting the hand away from the ticklish spot. He wonders if his mate has any spots like that and decides that he'll find out tomorrow. Maybe along with more spots that draw out those pretty noises like he made in the cave. With all the plans he had, tomorrow was shaping up to be a very good day indeed.

“Draw? What draw?” he asks, confused. He keeps them heading towards the boat but at a slow pace, knowing that they're within hearing range of his Uncle at least, since their language carried a lot further in the water than the human one. The young mer would be able to hear Thorin telling him to hurry up even though the boat is still a speck in the distance.

“Tell Uncle and Dwalin, mates?” Kíli asks a little worried. If he was asked outright he wouldn't lie but keeping it a secret for at least a little while wouldn't hurt. He knew how his own guardians would react but he barely knew Dwalin. It was easy to imagine that he would be angry that his son was mates with a mer, and that he would try to keep them apart.

"We probably should. They'll be angrier if they find out later," Fíli sighed, burying his nose in the soft hair at the back of Kíli's neck, breathing in the smell of the ocean that clung to the brown strands. "Better to get it over with now than to put it off and dread it."

He's smiling, though, at Kíli's confusion over the meaning of drawing, placing one last kiss to the soft skin of the mer's gills.

"Drawing is when you make a picture of something. In this case, I want to make pictures of you, so I can look at you whenever we're apart and remember you," he explained warmly. He watched as the boat got steadily larger and larger, and the figures of his Father and Thorin became more and more defined. 

Fíli had never been so unhappy to see them in his entire life.

Kíli nods as he swims up next to the boat, both Dwalin and Thorin watching the younger pair. He hopes that he and Fíli will never be apart long enough for the human to forget him but after they announce that they're mates, having those pictures might be a good thing.

“Well at least you brought him back in one piece, and on time,” his Uncle chuckles in their language, smiling from the other side of the boat. The younger mer roles his eyes but makes sure to keep the boat between him and Thorin while also staying out of arm's reach of Dwalin. The wooden vessel won't keep his Uncle from him for long but it'll give him a head start if he needs it.

“What did you do together? Did you do something besides go swimming?” His Uncle prods, this time in the human language. Kíli looks between the other three, eyes landing on Fíli before he answers.

“Uhm. Fíli and Kíli, mates now,” he answered with a warm smile at his mate. Kili's pretty sure the long, exasperated sigh his Uncle gives can probably be heard all the way back home by his Mother.

“Of course. I left you alone for a few hours,” Thorin continues to sigh as he rests his forehead against the boat.

Dwalin isn't quite as sedate about it as Thorin, however, staring at Fíli with his eyes bugging out of his head and his mouth ajar.

"You did _what_!?" he, admittedly, shrieked, making Fíli wince at the shock and anger in his Father's voice, fingers tightening their grip on Kíli's shoulders.

"We mated, Pa. Kíli is my mate, now," Fíli said firmly, giving the older man a stare to curdle milk. He was finally taking charge of his life for the first time since his Mother died, and he wasn't about to listen to anyone that tried to tell him this was wrong.

Dwalin could tell that Fíli wasn't about to budge on the topic, especially not if he started yelling, so he forced himself to level back out, breathing hard through his nose.

"Fíli, you've known him for a day. Why on earth would you become his mate?" he said finally, voice much more even than it had been before, though still a bit more pitchy than was normal.

Fíli swallowed thickly and rested his forehead against the back of Kíli's head, breathing in the clean smell of his mer.

"Because of the singing. The moment I saw him there was this music in my head and it felt like if I didn't have Kíli then there was nothing left in the world that mattered," he admitted softly.

"I needed to have Kíli and until I did there was nothing else."

Kíli swims back closer to the boat so that Fíli can get in if he wants, having moved away when Dwalin started to yell to try to protect his mate from his anger, as his Uncle makes a low noise of understanding. He tries to hide the smile that wants to form on his lips from the two elders. He'd known that Fíli had heard his song, but he hadn't know that he'd heard it from the moment they laid eyes on each other. It makes him feel a little giddy to know that his mate wanted him at the same time that the mer had wanted his human.

“Did you tell him about the song?” his Uncle whistles at him in their language. Kíli starts to nod but then shakes his head. 

“He mentioned it first, that he could hear it but not until after we decided to be mates. I told him that's why he could hear it. I didn't know he heard it when we met,” he replies. Thorin sighs again but nods this time.

“Not happy about it but won't keep you apart either.” His Uncle finally decides. That's better than what Kíli had been hoping for, of course there is still his mother to deal with, now it's just a matter of what Dwalin says.

Fíli hauls himself into the boat while his Father and Thorin talk quietly, pulling on his thankfully dry clothes and boots. He was shivering now that he didn't have Kíli's body heat to warm him up and he was grateful for the layers. Not to mention that, after many hours in the water, his skin had shriveled into a prune.

He stiffens when Dwalin turns back to look at him, but relaxes warily when there's a weary smile on his face.

"While I wish you had given it more time before you leapt head first into an unbreakable bond with another species... I understand and give you permission to continue this courtship," he sighed. A wide grin split Fíli's face and he leaned in to knock their foreheads together, squeezing his Father's shoulder warmly.

That part done, he turns to wrap his arms around Kíli and drags the mer up into the boat and onto his lap, crushing their mouths together. If Thorin and Dwalin are put out by this in any way he doesn't even notice, enraptured in the taste of his mate on his tongue.

Kíli is surprised, both by being suddenly grabbed and his mates strength, but ends up laughing as Fíli hauls him up into the boat. He's instantly got his tail curled around Fíli's middle while his arms are wrapped around his shoulders. He doesn't care that their guardians are still there either, too happy with being able to stay mated to Fíli to bother with the older pair.

At least until there's distinctly annoyed growling from the side of the boat. 

“You still have to explain this to your mother,” his Uncle says coolly. The younger mer breaks their kiss with a nervous laugh and even though he still has to face her, he can't stop smiling while he's still wrapped around his mate.

“See tomorrow?” Kíli asks as he leans his forehead against the human's, like he'd seen Fíli do with Dwalin. He decides that he likes doing this, he's able to look at his mate's blue eyes and is close enough to steal another kiss. Which he does, much to his Uncle's annoyance.

The young mer is slow to unravel from Fíli but eventually makes it back into the water, where his Uncle waits with a generally displeased look, although there's something in his blue eyes that makes Kíli think that Thorin might actually be a little happy for the younger pair.

"See tomorrow," Fíli promises, leaning down to press one last kiss to his mate's forehead, smiling a little wickedly when he withdraws.

"If your Mother lets you live, that is," he adds with a laugh, ducking to avoid the splash of water Kíli sends his way at the teasing. He grows somber, though, at the sight of the two mer swimming away, and he sits and watch in silence with his Father until they're gone beneath the rippling water.

He breaks the silence when they've begun to row back towards the shore, still staring at the darkening horizon and feeling lost despite himself. 

He'd never quite understood why it'd taken Dwalin so long to say his goodbyes to Thorin, but, he was starting to get now just how difficult it was to be parted from one's mate. 

Fíli looked up at the darkening sky and smiled when he saw the stars starting to appear in the darkness. 

They reminded him of the strange glowing lights on the ceiling of their cave and the sight of his mate, awash in blue and white, looking at him as if he'd hung the sun in the sky. 

"Tomorrow," Fíli said aloud, drawing his Father's attention from the beach ahead of them. He missed the warm look Dwalin gave him, staring intently at the stars as he was, but feels the weight of his hand on his knee.

"Tomorrow," he echoes and slowly rows them home.

Tomorrow.

**Author's Note:**

> We both loved the idea that mer are fascinated by butts that kyuubikun and ladynorthstar drew, so we decided to include it here because butts are pretty great.
> 
> Title inspired by Beauty and the Beast lyrics because why not!


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